In the majority of cases, modern motor vehicles are equipped with brake systems in which the brake pedal pressure is transmitted to the brake cylinders—mostly boosted by a brake booster—by way of hydraulic lines. In motor vehicles of the next generation, the motion signal of the brake signal generator, upon the driver's request for braking, will not be transmitted exclusively hydraulically to a (hydraulic or electric) brake control device but by means of electric lines (these systems are commonly known as brake-by-wire systems). In addition to an electric signal transmission in the electro-hydraulic brake (EHB), a hydraulic line may be provided in addition to the electric line between the brake pedal and the brake control device for an emergency operation.
Very high demands are placed on the reliability of operation of a motor vehicle brake system. This also requires from the electronic acquisition of the position of a brake signal generator to be as accurate and reliable as possible.
An electronic system for acquiring the position of a brake signal generator must also exhibit a low consumption of rest current to prevent the usually limited energy capacity of an energy accumulator in the motor vehicle from being excessively stressed. Further, a corresponding system is required to permit being activated quickly and reliably when a request for braking pressure occurs due to movement of the brake signal generator, or when other outside events such as starting of the engine lead to conclude that a braking pressure request is imminent.
Systems for transmitting a brake signal are known in the art wherein potentiometers are used to sense the absolute position of the brake pedal and the position signal is transmitted to a processing unit in an analog manner. These systems suffer, among others, from the shortcoming that they are especially susceptible to disturbances. Further, the transmitted position signals are not sufficiently precise or permanently available, respectively, due to the hysteresis and wear of the potentiometer contacts.
Still further, active systems for travel measurement are known apart from the above-described passive systems, the said active systems being considerably more sophisticated in terms of circuit technology and, consequently, exhibiting a rest current consumption which is too high for continuous service.